An optical scanning device includes a light emitting portion, an aperture member formed with apertures, a cylindrical lens, and a polygon mirror. In the optical scanning device, laser beams emitted from the light emitting portion pass through the apertures formed in the aperture member, which restrict their beam width. Then, the laser beams pass through the cylindrical lens, are collected on and are reflected by the rotating polygon mirror, are deflected in a main scanning direction and scanned on a photosensitive member.